Build, sync and use debuggerd and su in ART's Android root testing dir.

Binaries /system/bin/debuggerd and /system/xbin/su are used by script
tools/run-jdwp-tests.sh as part of the process dumping command when
testing on device.

Note that this dumping command won't work on ART Buildbot devices
running Android N regardless, as the debuggerd protocol changed in an
incompatible way in Android O.

Test: tools/run-jdwp-tests.sh --mode=device
Change-Id: I402918ca0879583a1beb2dc71dc1d81516607ed2